AND VARNISHES Paint, including painting and the care of paints, is an important sub ject. Both the inner and outer walls and the floors of houses and most articles of furniture are painted. Hence a knowledge of the nature and properties of paint, both before and after its application, enables it to be put to a thousand practical uses in the household. The uses of paint are twofold, i. e., to protect the wood and other materials to which it is applied, and also to decorate them. The ingredients of paint are of two sorts: the pigments or coloring mat ter, chosen mostly for decoration; and the vehicle chosen to hold the color ing matter in suspension, and also, when desired, to furnish the requisite protection.
In mixing paints the various pig ments are chosen according to the col or wanted, and the different vehicles according to the use to which the paint is to be put.
Linseed Oil for Paints.—The best vehicle for paints used to protect woodwork and other surfaces from moisture and decay is linseed oil. This is one of the so-called drying oils which, on exposure to the air, absorb oxygen and form a resinous varnish that closes the pores and excludes the agents of destruction from all sur faces to which it is applied. Thus it holds the pigments in a firm water proof varnish.
Linseed oil is of two sorts: raw and boiled. The raw oil is of two grades: the cold-drawn and the hot-pressed or ordinary quality. Raw linseed oil dries slowly, passing through a gum my or sticky stage before acquiring a hard, resinous surface. The object of boiling this oil with oxide of lead, peroxide of manganese, and borate or acetate of manganese is to cause it to dry more quickly. Boiling gives the oil a dark or high color. The raw oil is obtained from flaxseed by crush ing the seed under great hydraulic pressure. When the seed is not heat ed, the oil is said to be cold-pressed or cold-drawn, and is of a light or pale color, but when the crushed seed is heated and pressed hot, the oil is darker. Much more oil can be ex tracted from the same quantity of seed by hot pressure. The cold-drawn oil is therefore more expensive, but it is of a better quality.
Pigments for Paint.—The pigments or coloring matter used in paints are prepared by grinding them in a mill and mixing them with a small quan tity of raw linseed oil. They come in small packages and are prepared for use by mixing them with an addition al quantity of raw or boiled linseed oil and one or more colored pigments, which are mixed together to produce any desired shade.
Thinners for Paints.—The various pigments mixed with oil alone would make too thick a coating; hence other ingredients known as thinners are em ployed to dilute them. These are oil of turpentine and benzine, which mix freely with linseed oil and various pigments, and reduce them to any de sired consistency.
Dryers for Paints. — Even boiled linseed oil does not dry quickly enough; hence to hasten the union of oxygen with the paint, which transforms it into a dry, hard, resinous substance, it is usual to mix paints with certain substances known as dryers. Among these are sugar (acetate) of lead, red lead, verdigris, binoxide of manganese, sulphate of zinc, etc. The most pow erful dryer is boric manganese, even the part being enough to greatly hasten the drying of linseed oil. These and other dryers come ground in oil ready to mix with paint.
Ready-made Paints.—The materials used for paints for home use must be kept separate and not mixed until the paint is about to be used. Or, if mixed in advance, the paint must be covered with water and kept from the air. Otherwise the thinner will evapo rate, the pigment will settle to the bottom, and the oil will become thick and ropy, forming a. hard skin over the top which cannot be dissolved. Hence paints are now mixed in fac tories on a large scale by a process which forms an emulsion or perma nent mixture of the pigment and the oil, and these can be had in any size cans, the contents of which are al ways ready for use. However, any one can obtain the necessary ingredi ents, pigment, oils, thinner, and dryer, and mix paints for home use at less cost usually than he would have to pay for the ready-made article, and with the further advantage of know ing precisely the nature and purity of all the ingredients employed.
Water-color Paints.—Paints for in terior work, walls, ceilings, pictures, maps, and the like, are sometimes pre pared without oil by using as u vehi cle glue or gum dissolved in water. After the water evaporates, the glue or gum is left, and this causes the pigments to adhere to the surface. The ingredients must not be mixed until ready for use, as glue or gum will not keep in solution for any length of time.
Calcimine is u paint of this char acter, being a mixture of prepared chalk with a solution of glue and various colored pigments.
Water colors can also be obtained in the form of cakes consisting of pigments and gum in solid form, which may be liquefied by dissolving in water or by rubbing them with a wet brush.
Paints — Other Ingredients. — Be sides linseed oil, for finer kinds of work, as the preparation of artist's colors, other oils, as nut and poppy oils, are sometimes used.
Miseellaneous Ingredients. — Solu ble glass, naphthas, tars, lime, and various other materials are sometimes employed for cheap paints or for special purposes. Poisonous sub stances are sometimes mixed with the paint used about salt water to pre vent marine plants and animals from fastening to painted surfaces, and phosphorus is sometimes added when a luminous paint is desired.